Hepatic steatosis (fatty liver) is an early and reversible stage of both alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD), which are major causes of liver-associated illness and death. However, unchecked hepatic steatosis can advance to irreversible steatohepatitis, fibrosis, cirrhosis, and ultimately hepatocellular carcinoma. Our objective is to elucidate the mechanisms leading to fatty liver, develop a biomarker signature of fatty liver to aid early diagnosis, and identify molecular targets for intervention at this early and reversible stage of liver diseases. Our preliminary studies suggest that diminished S-adenosylmethionine (SAM)-mediated methylation of cellular molecules is responsible for fatty liver because rats given a SAM precursor-deficient diet demonstrated hepatic steatosis and hypomethylation of lipids. We hypothesize that decreased cellular methylation leads to fatty liver, which can be characterized by an altered lipid metabolome (lipidome), especially decreased methylated lipids, to serve as a biomarker signature of steatosis. Metabolomics will be used to test this hypothesis in rats where methylation of biomolecules is compromised by a SAM precursor-deficient diet (aim 1), a situation exacerbated by alcohol consumption (aim 2), and which can be reversed by dietary supplement (betaine) (aim 3). Lipid-associated changes of the metabolome and proteome (in biosynthesis, degradation and transport) will be correlated in the plasma and liver so that plasma changes can serve as a biomarker signature of hepatic steatosis. This project will be conducted by an experienced multidisciplinary team including lipid chemists/biochemists, a hepatologist, a pathologist and bioinformatricians. Our results should establish that SAM deficiency is central to liver steatosis and exacerbated by alcohol abuse. By using trans-omic techniques (metabolomics, proteomics and genomics) we will identify a novel biomarker signature (methylated lipids) of hepatic steatosis which can ultimately be utilized for diagnosis of steatosis. Furthermore, the sequence of events leading to fatty liver identification by these trans-omic techniques should identify molecular targets for an early intervention. Health Relevance: Fatty liver is an early and reversible stage leading to both alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD), major causes of liver-associated deaths. This project will identify biomarkers of fatty liver for an early diagnosis, and also potential targets for the development of new drugs to prevent ALD and perhaps NAFLD.